Psychological stress is a causal factor in the pathogenesis of substance use disorder (SUD) and relapse risk. Low-income women report high levels of stress in SUD residential treatment stemming from significant economic and family stressors in addition to challenges adjusting to residential treatment demands. Unmanaged stress, especially in early stages of residential treatment, is a major concern because it can increase dropout. Dropout from residential treatment places women at risk of substance use relapse. A gap in knowledge persists regarding the use of mindfulness-based interventions (MBIs) with racially and ethnically diverse low-income women with SUDs, especially regarding the efficacy of adapted MBIs for preventing residential dropout and decreasing relapse. The long-term goal of this application is to improve treatment outcomes in Black, Hispanic and White low-income women with SUDs by targeting stress, residential dropout, and relapse. We have fully adapted, developed, and pilot tested a novel MBI, Moment-by-Moment in Women's Recovery: Mindfulness Based Relapse Prevention for Women (MBRP-W), that supports the needs of women in residential treatment. It showed promising results in substance use and perceived stress outcomes and no racial or ethnic differences in outcomes. This MBI integrates relapse prevention, addresses literacy level, and is relevant to issues surrounding treatment- and relapse-related stressors of disadvantaged women. The central hypothesis will be tested by pursuing three specific aims: (1) to test the efficacy of MBRP-W on residential treatment (a) retention and (b) substance use relapse in Black, Hispanic and White low-income women to determine; (2) the mechanisms of change underlying the MBRP-W program; and (3) if changes in hair cortisol as a marker of chronic stress provide a more powerful measure of stress compared to self- reported stress as a mechanism of change. A rationale for MBRP-W is the need for self-initiated stress management skills in women with SUDs during the early stressful periods of residential treatment that increase risk of dropout and relapse. The unique strengths of this application are its focus on underserved populations, residential dropout, and relapse outcomes, and the first-ever inclusion of a chronic stress biomarker in MBI research in the form of hair cortisol. The proposed work is innovative in that it intends to reduce stress in women to improve both retention and relapse outcomes. The expected results will define a viable integrative treatment that can improve stress management skills and treatment outcomes and will evaluate the utility of a biomarker of chronic stress. Results of this study will have a positive impact on substance use recovery outcomes in diverse groups of low-income women and identify mechanisms of action to inform future SUD treatment. The project's public health impact meets NIDA goals because it intends to prevent the escalation of addiction and its health consequences by offering a novel treatment accessible to undeserved women that is expected to decrease addiction-related racial and ethnic and gender-based health disparities.